This invention relates to a valve device for vacuum brake boosters of the type in which the pressure differential which becomes effective at a movable wall is controlled by a valve device provided within the bore of a control housing. The valve device has an annular flexible valve cone with an outer bead in sealing engagement with the bore of the control housing and which rests with its outer shoulder at the control housing. The valve cone has a radially inwardly extending valve flange which is biased by a valve spring to abut on a first valve seat arranged on a control piston movable by a piston rod. The valve flange upon movement of the control housing further cooperates with a second valve the seat of which is provided on a radially inwardly extending shoulder formed in the bore of the control housing. The valve device has a supporting ring provided with a cylindrical collar keeping the outer bead of the flexible valve cone in position at the control housing.
A valve device of the type in question is known from Laid-open German Patent Application-OS No. 1,601,707, in which the valve device has a reinforcing component. The reinforcing component has an annular member which keeps the outer mounting flange of the flexible valve body engaged with the wall and the outer shoulder of the bore. A flange bent upwardly is provided at the outer end of the annular member in order to accommodate the valve return spring. A flange directed angularly inwards is provided at the inner end of the annular member in order to accommodate and center the valve spring. One disadvantage among others of this known valve device lies in the differently proportioned forces with which the valve spring acts on the flexible cone valve, depending on the position in which the push rod for the actuation of the reaction piston is at each time. A further disadvantage lies in the fact that the valve return spring and the valve spring are arranged serially end to end so that the two springs altogether require the push rod to be comparatively long in order to accommodate them. This type of construction makes it difficult to configure a compact structure of the control housing and hence of the booster as a whole. Finally, the known design of the valve spring has the disadvantage that it does not exert any centering effect on the valve flange of the valve device and the valve spring itself tends to slip away when being compressed leading to leakages in the area of the valve seats.